Blasting device



Jan- 20, 195 s. H. DAVIDSON ET AL 2,869,462

BLASTING DEVICE Filed April f1, 1955 IN VEN TORS SAMUEL HENRY DA V/DSO/V DAV/D AUGHl/VVOLE LOVE HUGH THOMAS WILL l/JMS /WW MM ATTORNEYS BLASTIN DEVICE Application April 4, 1955, Serial No. 498,942 5 Claims. (Cl. 102-25) The present invention relates to an improved blasting device of the kind wherein a charge consisting essentially of a solid composition capable when locally heated of selfsustain'ing non-detonating exothermic gas-producing decomposition without liability to ignite methane air mixtures or coal dust is enclosed in a re-utilisable apparatus consisting essentially of a tubular container of pressure resisting construction provided at one end with a detachable electric firing head to which the local heating means are connected and at the other end with a detachable ported venting head from which the container is sealed otiby means adapted to yield at a predetermined pressure generated within the container by said decomposition.

The employment of blasting devices of this kind results in a comparatively gentle heaving action especially suitable for theproduction oflump coal and they can be used in fiery and dusty mines. Considerable use has been made inBritish coal mines of a device of this kind wherein the gas-producing charge consists essentially of a stabilised equimolecular mixture of sodium nitrite and ammonium chloride.

The decomposition of these particular compositions can be initiated at atmospheric pressure, for instance by .an electric blackpowder fuse, and it is usualto load them into thecontainer of the blasting device above ground.

It has also been proposed to employ as the gas generating charge certain compositions containing ammonium nitrate capable offiameless gas generating decomposition, and it is'possible to produce ammonium nitrate compositions of thiskind which ,will only support theird eco'rnposition atsuperatmospheric pressuresand are therefore suitable for underground loading in conjunction with nameless gas-producing local heating compositions. These compositionsgive less lash anda less dense fume thanthose basedon ammonium chloridersodium nitrite m tt t The objectof the presentinvention isto providedevices of tl1e aforesaid kind of sirnpl iiied construction lenable themitoheloadedunderground.

re order to expedite loading it would be desitablethat theschargeof the solid gas. generating compositionshould heenclosed in apackageithat canbe-s lippedinto thecon- -tainer'. Forv underground 7 loading. purposes it would. also bedesirable that only one of the threaded joints should require to be screwedup below ground andthataseal at' the joint involving themeans adapted toyieldat predetermined. pressure should beformed as theiinternal gas pressure develops. a

According to the present invention a blasting device of rhe kind in which a package containing a charge ot a nondet'onating gas-producing compositioii capable of s'eItEsustained and selfpropagating gas producing reactionlwhen merely locally heated and a" safetyigniter positioned for the initiation of slaid charge are enclosed in a rigid conta n t t ad d a bo e d h i -a sn snd se s-t t iin ih idid s s tlyth e d srs ny nfih is tl Patented Jan. 20, 1959 i the ported venting head has a cutting edge at its annular end and in that said rupturable separating means is of slightly deformable material which is adapted as the pressure increases in the portion of the container which is on tie side of the rupturable separating means further removed from the cutting edge to be pushed against and become indented by said cutting edge and thus to seal the cylindrical container until a pressure isbuilt up within the container suflicient to rupture said rupturable separating means.

if desired said package is integral with said rupturable separating means and is so positioned in the bore of the container that the rupturable separating means is nearer to said cutting edge. i

The safety igniter is usually so positioned with respect to the package that it can initiate the end of the charge which is further away from said cutting edge. The invention also includes blasting apparatus of readily assembled construction comprising a rigid container threaded at both ends having at one end a gas-tight firing head detachably threaded therein and havingat the other end a ported venting head detachably threaded therein separated from the container by a ruptur able separating means characterised in that the ported venting head had a cutting edge at its annular end and in that said rupturable separating means is of slightly deformable material which is adapted when the pressure is increased in the portion of the container which is on the side of the rupturable separating means further removed from the cutting edge to be pushed against and become indented by said cutting edge and thus to seal the cylindrical container until a pressure is built up within thecontainer sufficient to rupture said separatingmeans.

It is also desirable in said blasting apparatus thatthe bore of the container at the firinghead should not be less than that of the main portion of the container.

. As it is desirable to introduce the package from the firing head end the bore of the container at the firing head end should preferably not be less than that of the main portion of said container. It is indeed anadvantage of the invention that the bore of the container can be the same throughout its occupiable length.

The charge of the solid composition capable when locally heated of self-sustaining fiameless non-detonating exothermic gas-producing decomposition may consist for instance of a stabilised equimolecular mixture of an alkali metalenitrite and anammonium salt, forinstance a mixtureof sodium nitrite and-ammonium chloride containing from 1 to 3% of its weight of magnesium carbonate, but his preferable that the charge should be a composite charge whereof the priming portion is a flameless gas-producing heating composition capable of ignition by the safety igniter at atmospheric pressure and the remaining portion is a composition also capable of self-sustaining non-detonating exothermic gas-producing decomposition but only when a pressure substantially above atmospheric has been generated within said container by thedecomposition of the priming portion. In a composi e charge of this kind the portion whose decomposition can only be initiated at super-atmospheric pressure will not undergo decomposition should the package containing the charge be accidentally heated to a temperature sufiicient to'cause the more easily decomposed portion to decompose so long as the package has not been introduced into the container in which it is intended to decompose, and this enables the package containing the charge to be safely handled below ground in the mine. i

The cylindrical portion of the wall of the package employed according to the invention may conveniently be made of fireproof cardboard or paper or synthetic resin and the main charge may be such as to combust it within the container. The rupturable separating means can be in the form of a plug and the wider end surface of the plug can either form the forward end wall of the package, or be securely attached to the material forming the end wall. This plug may advantageously consist of a fabric reinforced synthetic resin or a hard rubber-like material that will disintegrate into small fragments when it bursts under the predetermined pressure. The wall of the other end of the package is preferably recessed to receive the safety igniter.

' In loading the assembly, the package with the plug having for instance a converging curved surface in front of it is pushed through the open rear end of the pressure resisting container to which the venting head has already been threaded, along the bore of said container, in which it is a push fit, preferably until'the curved converging surface of the plug bears against the cutting edge of the venting head. The friction between the cylindrical walls of the packaged charge and of the container will thus hold the plug in the requiredbearing position. The safety igniter, which is preferably already in the recess in the charge package, is attached to the terminals of the firing head, and the firing head is then screwed home.

The threaded joint between the firing head and the container is preferably of the kind in which the development of internal pressure in the container increases the effectiveness of the seal since this enables the joint to be made effective without applying high torque as by means of a vice, and so permits the operator to form the joint by hand after the blasting device has been loaded while partly in the borehole. An O-ring joint may be used for this purpose.

When the safety igniter is subsequently fired nd the charge within the package starts to decomposethe gases tend to drive the package and hence the plug further and further forward on to the cutting edge of the venting head and since the plug is of slightly deformable material the effectiveness of the seal increases as the pressure rises until the predetermined pressure at which the plug disrupts has been built up. Since the package is a push-fit within the container, the cylindrical wall of the package, so long as the fore part of it exists, tends to be pressed outwards and thus maintains the gas pressure directly behind the plug.

The invention is illustrated with reference to the diagrammatic drawing accompanying the specification and which drawing represents a longitudinal section of a blasting device in accordance with the invention.

In the diagrammatic drawing 1 is the cylindrical wall of a high tensile steel tube internally threaded at its forward end as shown at 2 and at its rear end as shown at 3. The venting head which is correspondingly threaded near to its open end terminates in a machined annular end face 5 making a solid angle of 90 with the smooth internal cylindrical wall 6 of the venting head 4.- The annular end face 5 thus makes a cutting edge with the internal cylindrical wall 6. The internal cylindrical wall 6 forms an axial gas channel which communicates with the exteri r through the rearwardly diverging ports 7. 8 is a gasket rendering the joint between the container 1 and the venting head 4 gas tight.

9 is a fireproofed cardboard cylinder closed at its forward end by a plug 10 of a fabric reinforced synthetic resin whereof the rearward cylindrical portion is cemented into the cardboard cylinder to form the end wall thereof and the forward frustoconical portion makes contact all around the aforesaid cutting edge. A charge 11 consisting of 160 grams of a mixture of 49% ammonium nitrate, 34% magnesium nitrate hexahydrate and 17% woodiiour is lightly tapped into the forward portion of the cardboard cylinder and a charge 12 consisting of 40 grams of a lightly packed safety priming composition based on a mixture of guanidine nitrate and potassium persulphate is introduced into the rear portion of the cardboard cylinder. Charge 12 is incapable of igniting a methane air mixture when the decomposition takes place even at atmospheric pressure and charge 11, which has sufficient available oxygen to combust the cylinder 9, is only capable of sustaining its own decomposition at a pressure somewhat above atmospheric. 13 is a safety initiator consisting essentially of an antimony/permanganate composition and an electric fusehead sealed in a copper tube which remains intact but reaches a dull red heat when fired. 14 is an end cap. 15 and 16 are insulated leading wires passing to a live terminal 17 and an earth terminal 18 on the firing head 19 externally threaded near the forward end into the threads 3 of the container. 20 is a groove between the forward end of this firing head and the threadsthereof and 21 is an O-ring made of a resilient polymerised chloroprene composition.

The available volume of the container is 680 cc. and the pressure at which the plug 10 is adapted to burst into fragments is 1400 kg./cm.

In loading the device the container 1 with the venting head 4 is inserted a convenient distance into the borehole with the venting head 4 forward. The package 9 7 containing the charges 11 and 12 with'the initiator 13 already inserted into it is then pushed into the container until the plug 10 which forms the end closure, makes contact with the solid angle, i. e. the cutting edge at the end of the venting head 4. The leading wires 15 and 16 are connected to the terminals 17 and 18. The firing head 19 is then screwed up by hand and the external firing cables (not shown) are connected to an exploder (not shown) and the device is pushed forward to its blasting position in the borehole. When the circuit is completed the initiator 13 is actuated and rapidly attains a dull red heat sufiicient to initiate the decomposition of the primer charge 12 which quickly generates a sufficient pressure in the container to enable the maincharge 11 toundergo self-sustained decomposition. The end cap 14 is blown out during the decomposition of the primer charge and the gas pressure developed in the container urges the plug 10 forwardly so as to become indented by the cutting edgeformed by the end face 5 and the inner cylindrical wall 6 of the venting head 4. This establishes an effectivegas seal at the forward end of the container until thepressure at which the plug 10 is intended to burst is attained. Thereupon the gases vent through the axial channel and the ports of the venting head 4 into the borehole and so produce the desired blasting action.

i Although the firing head 19 is only screwed up by hand the development of pressure in the container causes the O-ring 21 to be deformed in such a manner as to form a gas tight seal between the joint between the container 1 and the firing head 19. The plug bursts in about 5 seconds from the moment when the firing circuit is I completed.

The invention also includes a rigid container of pressure-resisting construction threaded at both ends having at one end a gas-tight firing head detachably threaded therein and having at the other end a ported venting head detachably threaded therein characterised in that the ported venting head has at its annular end a cutting edge which effects the indentation of slightly deformable ma terial when pressed against it.

What we claim is:

1. A blasting device comprising an elongated, rigid container having a bore therein, a ported venting head communicating with one end of said bore, an annular cutting edge adjacent said one bore end generally facing in the direction of the opposite end thereof, said cutting edge being concentric with said bore and of a diameter less than the diameter of said bore, a package comprising a charge of non-detonating gas-producing composition capable of self-sustained and self-propagating gasproducing reaction in response to local heating and a safety igniter positioned to initiate said charge, a plug of slightly deformable material carried by one end of said package, said plug having a frusto-conical surface of substantial extent for engagement with said cutting edge, said bore having a package receiving portion of minimum diameter therein extending from said cutting edge toward the opposite end thereof, said package being insertable plug end foremost into said bore through the opposite end thereof into a position wherein the frustoconical surface of said plug is in engagement with said cutting edge, said package having a diameter substantially equal to the minimum diameter of said bore portion so as to be retained in said portion by friction, and a gas-tight firing head detachably secured to said container and closing the opposite end of said bore so that upon an increase in pressure in said bore as a result of the initiation of said charge escape of such increased pressure from said bore will be prevented by said firing head and by the engagement of the frusto-conical surface of said plug with said cutting edge until sufiicient pressure is built up in said bore to shear said plug.

2. A blasting device as defined in claim 1 wherein said annular cutting edge is formed on said ported venting head, said ported venting head being detachably threaded on said container adjacent said one bore end in concentric relation thereto.

includes a cylindrical portion forming an end of said' package and a frusto-conical portion providing said frusto-conical surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,602 Taylor Sept. 9, 1941 2,648,283 Coursen et al Aug. 11, 1953 2,650,540 Bugg Sept. 1, 1953 2,732,800 Coursen Jan. 31, 1956 FOREIGN PATENTS 689,440 Great Britain Mar. 25, 1953 654,958 Great Britain July 4, 1953 724,060 1955 Great Britain Feb. 16, 

